Comparative impact of replacing fish meal with azolla on growth, water quality, and physiology of red tilapia fingerlings at varying salinities

A 210-day experiment to assess the efficacy of substituting azolla plant powder at levels of 0, 20, 40, and 60% for fish meal on red tilapia fingerlings (RTF, initial weight of 18.23 ± 0.12 g) performance under salinity levels of 5, 18, and 28ppt. Among the various conditions, RTF-fed 20% azolla at 28 and 5ppt salinity showcased the highest specific growth rate (SGR), whereas the lowest SGR was observed in fish-fed 60% azolla at 5ppt salinity. Upon azolla incorporation, noteworthy elevations in phytoplankton, zooplankton, dissolved oxygen (DO), pH, NH₃, and NO₃ were noted and conversely, azolla introduction led to decreased NH₄ and NO₂ concentrations in all salinity levels. Further, a significant (p < 0.05) interaction between azolla levels and water salinity (S×A) significantly impacted the hematological parameters of RTF. The highest levels of superoxide dismutase (SOD), catalase (CAT), and total protein (TP) were found in RTF-fed 20% azolla at 28ppt salinity, while the lowest CAT and TP levels occurred in RTF-fed 60% azolla at 5ppt salinity. The highest aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were recorded in the RTF group fed 60% azolla at 5ppt salinity, with the lowest values seen in the group given 20% azolla at 28ppt salinity. RTF fed a 20% azolla diet at 18ppt salinity exhibited the highest lysozyme value, in contrast to the lowest value observed in the RTF group fed the control diet at 18ppt salinity. In conclusion, this study recommends the utilization of azolla at inclusion levels ranging from 20 to 40%, as it has the potential to notably enhance the immune system and elevate the survival rate of RTF.